Earth moving machines such as bulldozers, motor graders, scrapers, excavators, etc., are used to contour the ground for a variety of projects such as construction (e.g., roads, buildings, parks, and the like), mining, and agriculture. In order to achieve a pre-determined topography, it is important that soil is accurately removed from or added to selected areas. Therefore it is important to accurately control the operation of the working implement of the earth moving machine performing the contouring. More specifically, it is important to know the geographic location of the working edge of the implement (e.g., the bottom edge of a bulldozer blade) in 3 dimensions (e.g., latitude, longitude, and elevation) to accurately contour the site.
FIG. 1 shows a bulldozer 100 which uses a prior art positioning system to determine the location of the working edge 111 of blade 110. In FIG. 1, bulldozer 100 utilizes two masts (e.g., masts 112a and 112b), each of which are coupled with blade 110 and support a positioning system antenna (e.g., antennas 113a and 113b). Antennas 113a and 113b are used to receive data signals from a positioning system (e.g., global positioning system (GPS), GLONASS, etc.) to determine the position of working edge 111. For example, antenna 113a receives a GPS signal which is typically used to determine the geographic position of antenna 113a in 3 dimensions. Similarly, antenna 113b receives a GPS signal which is used to determine its geographic position in 3 dimensions.
Because the vector from antenna 113a to corner 111a is known, the geographic position of corner 111a can be derived using the geographic position of antenna 113a. Similarly, the geographic position of corner 111b can be derived. Using this information, the geographic position of working edge 111 can be derived.
One disadvantage to the positioning system of FIG. 1 is the necessity of using masts 112a and 112b to support antennas 113a and 113b. Antennas 113a and 113b are not typically mounted directly on blade 110 because soil piling over the top of blade 110 will damage antennas 113a and 113b. Additionally, the masts elevate antennas 113a and 113b to improve reception of the positioning system signals. Therefore masts 112a and 112b are used to isolate antennas 113a and 113b from this type of damage. However, when working in areas with overhanging tree branches and/or heavy brush, antennas 112a and 112b are still exposed to physical damage from the branches.
Another disadvantage of the positioning system of FIG. 1 is that the wires 114a and 114b coupling antennas 113a and 113b with a control unit 115 are exposed and susceptible to damage (e.g., from overhanging branches and/or brush). Additionally, antennas 113a and 113b are exposed to a significant amount of vibration when blade 110 is being used, which can damage the antennas over time.
FIG. 2 shows an exemplary motor grader 200 using a prior art positioning system similar to the positioning system described above with reference to FIG. 1. In the embodiment of FIG. 2, masts 212a and 212b couple antennas 213a and 213b with blade 210. In addition to the disadvantages discussed above with reference to FIG. 1, when used with a motor grader, masts 212a and 212b significantly restrict the range of motion of blade 210. For example, blade 210 can be rotated in 3 dimensions with respect to motor grader 200 and can be offset from the center line axis of motor grader 200 such that it extends to one side or the other of motor grader 200. Thus, a motor grader without masts 212a and 212b can typically extend blade 210 to the left until the right side edge of blade 210 is to the left of the center axis of beam 220 of motor grader 200. However, this range of motion for blade 210 is prevented in the embodiment of FIG. 2 by masts 212a and 212b. 
Using contact-based measurement systems to determine the position of the blade are disadvantageous in that they require some or all of: stepper motors, potentiometers, accelerometers, etc., to determine the position of the blade. These components can be incorporated into the machine when it is built, or an after-market kit can be installed upon the vehicle. However, incorporating these components into the machine when it is built can be too expensive for some users and the after-market kits are still subject to the damage as described above.